Inverter-Based Generators as Potential Flexible Resources for the Provision of Ancillary Services

The continuous increase of Inverter-Based Generation (IBG), mainly fed with non-programmable renewable energy sources, brings about a progressive phase out of large fossil-fueled plants equipped with synchronous generators, which usually supply ancillary services to control grid frequency and voltage. Therefore, attention is placed here on the flexibility that IBG itself could provide as reserve margins to support stability and security of the power system. An estimate is made of the potential flexibility of ground and rooftop PhotoVoltaic (PV) systems, plus rooftop PV with battery energy storage systems, and of onshore and offshore wind farms, for a 2030 scenario of the Italian power system. Potential downward and upward power margins are computed, for different deloading levels with respect to the expected available power output; this latter is obtained from annual stochastic power profiles with hourly time step for each IBG technology for each market zone. The analysis is carried out with reference to each hour of the day in each month, in terms of the 2.5% percentile of the power margins that could be obtained, i.e. the minimum flexibility which could be guaranteed with probability 97.5%. Results show that, in per unit of the installed capacity, PV technologies, especially ground PV and rooftop PV, exhibit significantly more flexibility than wind ones; this occurs also in absolute terms (i.e. in MW), due to the PV large installed capacity.